The present invention relates to hydraulic machines in general, and more particularly to improvements in external gear type pumps or motors.
In an external gear pump or motor, the stubs of the gears are received in bores, bearing sleeves or eight-shaped bearing members of the housing. It is already known to provide the housing of an external gear type pump with two recesses communicating with the outlet port and receiving relatively narrow inserts which are subjected to the pressure of fluid in the outlet port and urge the gears against the internal surface of the housing. The inserts normally consist of a suitable metal (e.g., sheet metal) and serve to establish desirable metallic seals for the paths wherein the fluid is conveyed from the inlet port toward the outlet port.
A drawback of presently known external gear pumps which embody the just discussed inserts is that the inserts transmit substantial forces which cause the teeth of the respective gears to bear against the internal surface of the housing with attendant pronounced wear upon the housing and gear teeth. Moreover, such substantial forces are transmitted to those surfaces of the housing which surround the stubs of the shafts for the mating gears. The resulting wobbling affects the output of the machine and the bearing surfaces for the stubs are subjected to excessive wear. Consequently, such surfaces must be provided on parts which consist of expensive highly wear-resistant material and the dimensions of the housing must be increased for the express purpose of insuring that the bearings for the stubs will exhibit a requisite resistance to stresses which are being transmitted by the gears in response to transmission of hydraulic forces via inserts in the region of the outlet port.